Probing gluon shadowing with forward photons at RHIC

TL;DR

This paper investigates how forward prompt photon production in RHIC collisions can constrain nuclear gluon distributions at small x, aiding in understanding nuclear parton densities and non-linear QCD effects.

Contribution

It demonstrates the sensitivity of prompt photon production at RHIC to nuclear gluon modifications using NLO calculations with nDSg densities.

Findings

R_dAu ratio can be measured with high statistical accuracy.

Prompt photon production is sensitive to nuclear gluon modifications.

Large counting rates enable precise measurements.

Abstract

There is a major need to better constrain nuclear parton densities in order to provide reliable perturbative QCD predictions at the LHC as well as to probe possible non-linear evolution at small values of x. In these proceedings, we discuss how the production of prompt photons at large rapidity in p-p and d-Au collisions at RHIC (sqrt(s_NN)=200 GeV) is sensitive to the nuclear modifications of gluon distributions at x~0.001 and at rather low scales, Q^2~10 GeV^2. The nuclear production ratio, R_dAu=sigma(d+A->gamma+X)/(2A sigma(p+p->gamma X), is computed for isolated prompt photons at NLO using the nDSg nuclear parton densities, in order to assess the visibility of the signal. We also emphasise that the expected counting rates in a year of running at RHIC are large, indicating that R_dAu could be measured with a high statistical accuracy.